linux-kernel - Re: [PATCH V2 2/2] cpufreq: Change freq before suspending governors

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Message-ID: <2065978.h16hV1Cgky@vostro.rjw.lan>
Date:	Sun, 24 Nov 2013 22:32:13 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Stephen Warren <swarren@...dotorg.org>,
	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Stephen Warren <swarren@...dia.com>, Kukjin Kim <kgene@...nel.org>,
	Amit Daniel Kachhap <amit.daniel@...sung.com>,
	Sachin Kamat <sachin.kamat@...aro.org>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	Patch Tracking <patches@...aro.org>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lan Tianyu <tianyu.lan@...el.com>, Nishanth Menon <nm@...com>,
	jinchoi@...adcom.com,
	Sebastian Capella <sebastian.capella@...aro.org>,
	Peter De Schrijver <pdeschrijver@...dia.com>
Subject: Re: [PATCH V2 2/2] cpufreq: Change freq before suspending governors

On Friday, November 22, 2013 12:39:24 PM Stephen Warren wrote:
> On 11/22/2013 05:52 AM, Viresh Kumar wrote:
> > On 22 November 2013 18:07, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> >> On Friday, November 22, 2013 04:59:49 PM Viresh Kumar wrote:
> >>> Some platforms might want to change frequency before suspending governors. Like:
> >>> - Some platform which want to set freq to max to speed up suspend/hibernation
> >>>   process.
> >>> - Some platform (like: Tegra or exynos), set this to min or bootloader's
> >>>   frequency.
> >>>
> >>> This patch adds an option for those, so that they can specify this at call to
> >>> ->init(), so that cpufreq core can take care of this before suspending system.
> >>>
> >>> If this variable is not updated by ->init() then its value would be zero and so
> >>> core wouldn't do anything.
> >>>
> >>> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> >>
> >> I don't think this is generally necessary, because the suspend/resume routines
> >> added by patch [1/2] will be executed very late during suspend or very early
> >> during resume and it shouldn't really matter what performance levels the CPUs
> >> are at then.
> > 
> > There are few things here:
> > - I feel that the current place from where we have suspended stuff is not gonna
> > fly. We are doing that in noirq and probably devices which might be required
> > during frequency transitions might already be down.. So we *may* need to
> > move that in dpm_suspend()..
> > - Secondly I want to understand why Tegra/Exynos has such code which I
> > mentioned above..
> > 
> > @Stephen, Kukjin and other samsung folks: Please provide some input here,
> > before your systems break in mainline :)
> 
> I believe we set the clock to a low value because fast clocks consume
> more power. Tegra architecturally supports a number of different suspend
> levels. Only some of those actually power off or gate the clock source
> itself.

Hmm.

Viresh, maybe make it possible for the cpufreq driver to provide suspend/resume
callbacks to be executed by cpufreq_suspend() and cpufreq_resume() introduced
by [1/2]?  Then Tegra could set the frequencies to what it wants from there
before the governors are stopped.

Thanks!

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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